23.—(1) A trustee is not liable for any act or default of the agent, nominee or custodian unless he has failed to comply with the duty of care applicable to him, under paragraph 3 of Schedule 1—
(a)when entering into the arrangements under which the person acts as agent, nominee or custodian, or
(b)when carrying out his duties under section 22.
(2) If a trustee has agreed a term under which the agent, nominee or custodian is permitted to appoint a substitute, the trustee is not liable for any act or default of the substitute unless he has failed to comply with the duty of care applicable to him, under paragraph 3 of Schedule 1—
(a)when agreeing that term, or
(b)when carrying out his duties under section 22 in so far as they relate to the use of the substitute.